Purpose: :
During the years 2003 to 2008, a substantial increase in theincidence of Acanthamoeba keratitis (AK) was noted in a numberof countries. This rise has been associated at least in part,with the use of COMPLETE MoisturePLUS multipurpose solutionthat induces the encystment of Acanthamoeba parasites into immature/earlystage cysts. In an effort to understand the possible reasonfor the recent increase in the AK, the goal of this study wasto assess whether the pathogenic potential of immature cystsis greater than that of Acanthamoeba trophozoites and maturecysts.

Methods: :
To determine whether the a major virulence protein of Acanthamoeba,the mannose-binding protein (MBP), that mediates the adhesionof amoebae to the surface of the cornea plays a role in theprocess of encystment, the trophozoites were incubated in theencystment medium in the presence and absence of α-mannoseand the data were analyzed to determine whether inhibiting thefunction of the MBP by the competing sugar, mannose, preventsparasite encystment. In an effort to assess the pathogenic potential,the ability of Acanthamoeba trophozoites, immature cysts andmature cysts to withstand harsh conditions, bind to host cellsand produce cytopathic effect was investigated.

Results: :
The first step in the process of encystment, the clumping ofthe trophozoites, was inhibited by free mannose but not otherirrelevant saccharides. This suggests that Acanthamoeba MBPplays a role in the process of encystment. Both immature cystsand trophozoites expressed MBP, adhered to corneal epithelialcells and produced cytopathic effect. However, immature cystsbut not trophozoites were resistant to harsh conditions suchas sonication. Although, mature cysts were resistant to harshconditions, they expressed little MBP and did not bind to hostcells or produced cytopathic effect

Conclusions: :
Acanthamoeba MBP plays a role in the process of encystment.Immature cysts may be more pathogenic than trophozoites as theyare resistant to harsh conditions and have retained the abilityto produce cytopathic effect.